A commonplace optical pickup device is composed of a semiconductor laser for emitting light on an optical disk, optical components for branching a beam from the semiconductor laser or focusing it on the optical disk, and an optical detector for receiving the reflected beam from the optical disk.
The optical pickup device is mounted with components which emit heat during recording or playback including a laser drive circuit, high frequency module, optical detector and objective lens drive coil in addition to the semiconductor laser. The temperature of the optical pickup device is raised by these heat emitting components.
In a recording type optical pickup device having a function to record information onto an optical disk such as a DVD-RAM/R/RW or CD-R/RW, the outputs of the semiconductor laser provided in the optical pickup device and of the laser drive circuit which drives the laser are greater relative to the output of the optical pick up device, and their heat emission is substantial. In this recording type optical pickup device, the higher the recording speed, the greater output the semiconductor laser requires and, moreover, the higher the heat emission. Especially, where the recording speed of the DVD is eightfold or even higher, in order to transmit high quality high frequency signals to the semiconductor laser, it is necessary to mount the laser drive circuit with a circuit for generating a recording signal waveform known as write strategy. This generating circuit is conventionally built into a circuit on a circuit board of the optical disk device, and the mounting of this generating circuit on the optical pickup device further increases the heat emitted from the laser drive circuit.
It is also required to arrange the semiconductor laser and the laser drive circuit close to each other to ensure a high level of transmission path performance. The arrangement of these heat emitting components in proximity to each other invites a further temperature rise in that area.
The heat emission described above involves the risk of deteriorating the performance, reducing the durability and inviting erroneous actions of such components as the semiconductor laser and the laser drive circuit.
On the other hand in an optical pickup device, high optical characteristics relating to the operating wavelength of CDs or DVDs are required. Especially in a single optical pickup device which can record information of both types of media, including CDs and DVDs, the requirement for high optical characteristics applies to the operating wavelengths of both CDs and DVDs. In order to meet these requirements, the semiconductor laser needs to be positioned with high accuracy and fixed in that position. To satisfy this need, when the semiconductor laser is fixed, it is not placed in close contact with the pickup case but at a distance of a few hundreds of μm to a few mm where its positional accuracy can be secured, and fixed in this highly accurately positioned state by filling. the gap between it and the pickup case with an adhesive. This results in the problem that the conduction of the heat generated by the semiconductor laser is obstructed by the adhesive, and the heat cannot be sufficiently conducted to the pickup case via fixing members.
As a solution to this heat emission problem, an optical pickup is proposed, for instance, in the Japanese Patent Laid-Open No. 2003-22555 (Patent Reference 1). According to this Patent Reference 1, there is disclosed an optical pickup equipped with a slide base movably supporting an integrated optical element provided with a light emitting element, wherein the integrated optical element is mounted on a flexible substrate for use as transmission path formed of a metallic or thermally. conductive material, and heat is conducted by keeping this transmission path flexible substrate in contact with the cover of the optical pickup and the slide base.
[Patent Reference 1] Japanese Patent Laid-Open No. 2003-22555, pp. 1-3, FIG. 1
In the aforementioned optical pickup according to Patent Reference 1, heat emitted from the integrated optical element is conducted to the cover and the slide base via the transmission path flexible substrate on which the integrated optical element is mounted, but it is still unable to achieve a sufficiently high level of heat conducting performance. Thus the transmission path flexible substrate according to Patent Reference 1 involves a problem. Namely, when heat conduction from the integrated optical element is needed, not only the substrate itself may also be electrified and emit heat to obstruct heat conduction from the integrated optical element to the cover and the slide base, but also, if any other heat emitting component is connected to the heat conduction side, the heat conduction performance of the integrated optical element will be deteriorated by the thermal influence of this additional heat source.